The present invention relates to a refrigerating system, and particularly to a defrost control apparatus and method which initiates defrost operation by obtaining the difference between the temperatures in the vicinity of an evaporator when driving and halting a blow fan and comparing the difference in temperatures with a predetermined set value.
In conventional refrigerators, defrost operation is executed irrespective of the quantity of the frost produced at an evaporator whenever the predetermined time elapses. However, the quantity of the frost produced at the evaporator depends on temperature, humidity about an evaporator and the quantity of the foods stored in the refrigerator.
Therefore, the conventional apparatus have the following problems:
Even though little frost is produced because of low temperature, low humidity about an evaporator and the little quantity of foods stored in the refrigerator, defrost operation is executed at the predetermined interval, so that power is wasted due to the unnecessary operation of a defrost heater.
On the other hand, although much frost is produced because of the high temperature and the high humidity about the evaporator and the large quantity of foods stored in the refrigerator, defrost operation is not executed till the predetermined time elapses, so that the efficiency of heat exchange and cooling efficiency of the refrigerator are deteriorated, and the internal temperature of the refrigerator rises.
A typical example solving the problem described above is disclosed in Japanese Laid-Open Patent Sho 58-178171. This apparatus includes blow speed detection elements mounted at the inlet and outlet of an evaporator and thermistor attached in the proximity of the evaporator and in the inlet duct. Thus, an output signal of blow speed difference and an output signal of temperature difference are ANDed, and the output signal of the AND logic is the defrost start signal. This invention is different from the present invention in that the defrost start time is determined by detecting temperatures at the proximity of the evaporator and in the inlet duct and blow speeds at the inlet and the outlet of the evaporator.
Another example solving the problem described above is disclosed in Japanese Laid-Open Patent Sho 56-149568. This invention includes a thermistor mounted in the position corresponding to the permissible thickness of frost and a thermistor mounted on the evaporator and compares the two sensed temperatures, so that when the difference is less than the predetermined value, the defrost operation starts. This invention is different from the present invention in that it senses temperatures on the evaporator and in the position corresponding to the permissible thickness of frost irrespective of the driving and halting of the evaporator blow fan.
Still another example solving the problem described above is disclosed in U.S. Pat. No. 4,045,971. This invention includes a heat conducting means attached to an evaporator and an air duct embracing a heat conducting means and being made of opaque materials in which a photo-source and photo-detector are mounted. When the light emitted from the photo-source reflects from the heat conducting means, the photo-detector detects the reflected light. This invention determines whether or not to start the defrost operation depending on the reflected quantity of light. Also, this invention is different from the present invention in that it does not consider the state of the blow fan and detects the quantity of frost produced at the heat conducting means.